“it”引导主语从句和“it”做形式主语还有强调句型的区别：
it引导的主语从句，形式主语就是it，真正的主语在句子的后面，通常是to do的不定式短语。
而强调句的结构 it is/was+被强调部分+that/who+句子其余部分，结构词it is/was和that/who都是没有实际意思的，只是构成句子结构的词而已。这个强调句只能强调名词和代词，也就是主语和宾语，不能强调其他句子成分。
主语从句：It is kind of you to help me with my housework.
强调句：It is you who help me with my housework.
主语从句中it做形式主语的常见句型：
It + be + 形容词+主语从句，如：It is uncertain whether he can come to Jenny’s birthday party or not.
It + be + 名词词组 + 主语从句，这类名词有：a fact, a pity, a shame, an honour，a question等，如：It’s a pity that you missed the exciting football match.
It remains a question whether he will come or not.
It + be + 过去分词+ 主语从句，这类过去分词有：announced, believed, expected, hoped, decided, reported, said, shown等，如：It is reported that 16 people were killed in the earthquake.